Outlook Anywhere HTTP 500 error

I am receiving HTTP 500 errors when running tests from testexchangeconnectivity.com/
I have already uninstalled and re-installed the RPC proxy twice. When I go to https://webmail.mydomain.org/rpc/rpcproxy.dll I get page cannot be displayed. I have checked and verified that my SSL settings are correct in IIS and I have checked the authentication settings are correct as according to http://technet.microsoft.com/en-us/library/gg263433(v=exchg.80).aspx. Please help. Webmail is working as an interim workaround but this has been happening since last week and users are getting restless.